1. Field of the Invention
The present invention relates to communication systems and to a system and method for prioritizing transmission data from end users in such systems.
2. Description of the Related Art
A communication system facilitates two-way communication between a plurality of subscriber units (fixed and portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (“PCS”), cordless telephones, and wired systems. An objective of these communication systems is to provide communication channels on demand between the subscriber units and their respective base stations in order to connect a subscriber unit end user with the fixed network infrastructure. Some systems having multiple access schemes, a time “frame” is used as the basic information transmission unit. Each frame is sub-divided into a plurality of time slots. Subscriber units typically communicate with their respective base station using a “duplexing” scheme thus allowing for the exchange of information in both directions of the connection.
Transmissions from the base station to the subscriber units are commonly referred to as “downlink” transmissions. Transmissions from the subscriber units to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, wireless communication systems have typically used either time division duplexing (“TDD”) or frequency division duplexing (“FDD”) methods to facilitate the exchange of information between the base station and the subscriber units. However, such methods can also be used in wired systems.
These communication systems strive to maximize their utilization of their available bandwidth while also providing true bandwidth on demand to their users. However, when user bandwidth requests exceed the instantaneous available bandwidth, a selection process is utilized to determine which of the users will receive bandwidth at a given time. This selection process can be based upon, for example, a first-come-first-serve base where each user is treated similarly.
More recently, communications systems distinguish between different classes of service (CoS) or different quality of service (QoS) that are provided to the users. For example, some communication system that utilize Asynchronous Transfer Mode (ATM) systems offer CoS and/or QoS to their users. Other types of data traffic, for example, internet protocol (IP) can also be used in conjunction with CoS and/or QoS. For ease of explanation, the following description of various service categories uses terminology from an ATM based communication system. However, the systems and methods described below are not limited to an ATM based communication system. The typical classes of service are:
CBR—Constant Bit Rate. This service provides users with a constant quantity of bandwidth whether they use it or not. An example is voice over T1 services.
rt-VBR—Real-time Variable Bit Rate. This service allocates data on a demand basis. The demand basis can include average rate and/or peak rate usage. This service is often delay and jitter intolerant. Examples are voice over AAL-2 or Voice over IP (VOIP).
nrt-VBR—Non-real-time Variable Bit Rate. This service allocates data on a demand basis. The demand basis can include average rate and/or peak rate usage. This service is more delay and jitter tolerant than the rt-VBR service described above. VoIP and streaming video are sometimes implemented using this class of service.
MGR—Minimum Guaranteed Rate, sometime referred to as Guaranteed Frame Rate (GFR). This service is similar to the nrt-VBR service except that it includes a minimum committed rate. The minimum committed rate is guaranteed to be available when requested. MGR service further includes a peak rate. Demand greater than the committed rate but less than the peak rate is referred to as excess demand. Services such as streaming video are sometimes implemented using this class of service.
UBR—User Bit Rate, sometimes referred to as Available Bite Rate (ABR) or Best Effort. These services are very delay and jitter tolerant. An example is web surfing.
Communication systems that provide multiple classes of services to its end users are presented with having to prioritize transmission data while taking into account service characteristics for the classes of service.